1. Field of the Invention
This invention relates to grease compositions using novel triurea compounds which are excellent in oil separation, shear stability and oxidation stability at a high temperature and are noticeably stable in the structure of a thickening agent under severe conditions of oxidation or high temperature and the like.
2. Description of the Prior Art
Presently most broadly used greases are ones using a metal soap as a thickening agent and among them, lithium soap grease has been generally numerously used. However, greases having higher quality and longer durable life have been demanded as the lubricating conditions become more severe owing to the progress of machines and novel thickening agents having excellent thermal resistance and long durable life at a high temperature have been gradually developed.
Among the thus developed greases, urea greases are non-soap ones and contain an ashless thickening agent and therefore these greases are one of representable high temperature greases. In general, these greases are high in dropping point and are relatively stable in the structure of the thickening agent at a high temperature and contain no metallic atom which promotes the oxidation deterioration in the molecule of the thickening agent, so that the oxidation stability is generally high.
Urea compounds of the thickening agent may be produced by reacting an isocyanate with an amine in a solvent or a base oil but the urea compounds of the reaction products include a large number of urea compounds depending upon the number of urea bond ##STR2## ureilene radical), and the kind or number of radicals (hydrocarbon radicals, etc.) between the urea bonds and terminal radical of the compound, and there is a great difference in the grease property.
The most typical prior patents already reported comprise diurea grease by E. A. Swakon et al (U.S. Pat. No. 2,710,839, U.S. Pat. No. 2,710,840, U.S. Pat. No. 2,710,841) and tetraurea grease by J. L. Dreher et al (U.S. Pat. Nos. 3,242,210, 3,243,372) and the other many patents intend to develop these base patents and improve the grease properties.
However, in general the diurea greases have defects that at a high temperature the consistency softens and the oil separation is high and the tetraurea greases when exposing to a high temperature for a long period of time, readily cause the hardening of consistency. Furthermore, in the prior triurea greases (Japanese Patent No. 932,322), the consistency softens at a high temperature and in symmetrical triazine tetraurea greases (U.S. Pat. Nos. 4,026,890 and 4,113,640), the production of the thickening agent is troublesome and a long time is necessary for obtaining the final grease product.